This project is concerned with an analysis of the activity of nerve cells in that system within the primate brain which is necessary and responsible for the process we refer to as attention. Monkeys trained to perform visually-guided go, no-go discrimination tasks are tested while extra cellular recordings are made from brain regions thought to be part of an attentional system. The most recent study in this series examined structures in the forebrain. We have found attention-related units in the anterior portion of the upper bank of the cingulate sulcus and in the periarcuate area of the dorsal frontal cortex. These cells responded to the manipulation of attention, e.g., manipulation of the pre-stimulus waiting period or changing the behavioral significance of the task-stimuli. These attention-related units have properties similar to those found in the brainstem reticular formation in previous studies.